PhpStorm Debugger has stopped working

I've been using PhpStorm V9 EAP PS-141.332 since it was released on March 25th.
Been debugging as usual, as recently as yesterday afternoon.
Suddenly, today, the debugger no longer works.
- Project files are in a local directory on the Mac on which I run PhpStorm
- That directory is shared via NFS and is mounted on a virtual machine running Ubuntu
- When I do Run -> Start listening for PHP Debug Connections and then do a netstat -an, there is an active LISTEN on port 9000
- I made no configuration changes to erither PhpStorm or the VM prior to this happening

PhpStorm debug configuration:
- External connection:
     - Ignore external connections through unregistered server configurations: disabled
- Xdebug:
     - Debug port: 9000
     - Can accept external connections: enabled
     - Force break at the first line when no path mapping specified: disabled
     - Forst break at the first line when a script is outside the project: disabled
- Zend Debugger:
     - Can accept external connections: disabled

Path mappings shouldn't be an issue. The paths are identical on the Mac and the VM.

Suggestions?
Thanks in advance